text: /*
   * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without modification,
   * are permitted provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright notice,
   *    this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   * 3. The name of the author may not be used to endorse or promote products
   *    derived from this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
   * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
   * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
   * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
   * OF SUCH DAMAGE.
   *
   * This file is part of the lwIP TCP/IP stack.
   *
   * Author: Adam Dunkels <adam@sics.se>
   *
   */
  
  
  
  /* ip.c
   *
   * This is the code for the IP layer.
   *
   */
  
  
  #include "lwip/opt.h"
  
  
  #include "lwip/def.h"
  #include "lwip/mem.h"
  #include "lwip/ip.h"
  #include "lwip/ip_frag.h"
  #include "lwip/inet.h"
  #include "lwip/netif.h"
  #include "lwip/icmp.h"
  #include "lwip/raw.h"
  #include "lwip/udp.h"
  #include "lwip/tcp.h"
  
  #include "lwip/stats.h"
  
  #include "lwip/snmp.h"
  #if LWIP_DHCP
  #include "lwip/dhcp.h"
  #endif /* LWIP_DHCP */
  
  
  /* ip_init:
   *
   * Initializes the IP layer.
   */
  
  void ip_init(void)
  {
  }
  
  /* ip_lookup:
   *
   * An experimental feature that will be changed in future versions. Do
   * not depend on it yet...
   */
  
  #ifdef LWIP_DEBUG
  u8_t ip_lookup(void *header, struct netif *inp)
  {
      struct ip_hdr *iphdr;
  
      iphdr = header;
  
      /* not IP v4? */
      if (IPH_V(iphdr) != 4) {
          return 0;
      }
  
  #if IP_OPTIONS == 0
      if (IPH_HL(iphdr) != 5) {
          return 0;
      }
  #endif /* IP_OPTIONS == 0 */
  
      switch (IPH_PROTO(iphdr)) {
  #if LWIP_UDP
          case IP_PROTO_UDP:
          case IP_PROTO_UDPLITE:
              return udp_lookup(iphdr, inp);
  #endif /* LWIP_UDP */
  #if LWIP_TCP
          case IP_PROTO_TCP:
              return 1;
  #endif /* LWIP_TCP */
          case IP_PROTO_ICMP:
              return 1;
          default:
              return 0;
      }
  }
  #endif /* LWIP_DEBUG */
  
  /* ip_route:
   *
   * Finds the appropriate network interface for a given IP address. It
   * searches the list of network interfaces linearly. A match is found
   * if the masked IP address of the network interface equals the masked
   * IP address given to the function.
   */
  
  struct netif *
  ip_route(struct ip_addr *dest)
  {
      struct netif *netif;
  
      /* iterate through netifs */
      for (netif = netif_list; netif != NULL; netif = netif->next) {
          /* network mask matches? */
          if (ip_addr_maskcmp(dest, &(netif->ip_addr), &(netif->netmask))) {
              /* return netif on which to forward IP packet */
              return netif;
          }
      }
      /* no matching netif found, use default netif */
      return netif_default;
  }
  #if IP_FORWARD
  
  /* ip_forward:
   *
   * Forwards an IP packet. It finds an appropriate route for the
   * packet, decrements the TTL value of the packet, adjusts the
   * checksum and outputs the packet on the appropriate interface.
   */
  
  static void
  ip_forward(struct pbuf *p, struct ip_hdr *iphdr, struct netif *inp)
  {
      struct netif *netif;
  
      PERF_START;
      /* Find network interface where to forward this IP packet to. */
      netif = ip_route((struct ip_addr *)&(iphdr->dest));
      if (netif == NULL) {
          LWIP_DEBUGF(IP_DEBUG, ("ip_forward: no forwarding route for 0x%lx found\n",
                                 iphdr->dest.addr));
          snmp_inc_ipnoroutes();
          return;
      }
      /* Do not forward packets onto the same network interface on which
       they arrived. */
      if (netif == inp) {
          LWIP_DEBUGF(IP_DEBUG, ("ip_forward: not bouncing packets back on incoming interface.\n"));
          snmp_inc_ipnoroutes();
          return;
      }
  
      /* decrement TTL */
      IPH_TTL_SET(iphdr, IPH_TTL(iphdr) - 1);
      /* send ICMP if TTL == 0 */
      if (IPH_TTL(iphdr) == 0) {
          /* Don't send ICMP messages in response to ICMP messages */
          if (IPH_PROTO(iphdr) != IP_PROTO_ICMP) {
              icmp_time_exceeded(p, ICMP_TE_TTL);
              snmp_inc_icmpouttimeexcds();
          }
          return;
      }
      /* Incrementally update the IP checksum. */
      if (IPH_CHKSUM(iphdr) >= htons(0xffff - 0x100)) {
          IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + 2);
      } else {
          IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + 1);
      }
  
      LWIP_DEBUGF(IP_DEBUG, ("ip_forward: forwarding packet to 0x%lx\n",
                             iphdr->dest.addr));
  
      IP_STATS_INC(ip.fw);
      IP_STATS_INC(ip.xmit);
      snmp_inc_ipforwdatagrams();
  
      PERF_STOP("ip_forward");
      /* transmit pbuf on chosen interface */
      netif->output(netif, p, (struct ip_addr *)&(iphdr->dest));
  }
  #endif /* IP_FORWARD */
  
  /* ip_input:
   *
   * This function is called by the network interface device driver when
   * an IP packet is received. The function does the basic checks of the
   * IP header such as packet size being at least larger than the header
   * size etc. If the packet was not destined for us, the packet is
   * forwarded (using ip_forward). The IP checksum is always checked.
   *
   * Finally, the packet is sent to the upper layer protocol input function.
   */
  err_t ip_input(struct pbuf *p, struct netif *inp)
  {
  
      static struct ip_hdr *iphdr;
      static struct netif *netif;
      static u16_t iphdrlen;
  
      iphdr = p->payload;
  
      if (IPH_V(iphdr) != 4) {
          pbuf_free(p);
          return ERR_OK;
      } /* end if */
  
      iphdrlen = IPH_HL(iphdr);
      iphdrlen *= 4;
  
      if (iphdrlen > p->len) {
          pbuf_free(p);
          return ERR_OK;
      } /* end if */
  
      /* verify checksum */
  #if CHECKSUM_CHECK_IP
      if (inet_chksum(iphdr, iphdrlen)) {
          pbuf_free(p);
          return ERR_OK;
      } /* end if */
  #endif
  
      pbuf_realloc(p, ntohs(IPH_LEN(iphdr)));
  
      for (netif = netif_list; netif; netif = netif->next)
  
          if (!ip_addr_isany(&netif->ip_addr)) {
  
              if (ip_addr_cmp(&iphdr->dest, &netif->ip_addr) || (ip_addr_isbroadcast(&iphdr->dest, &netif->netmask) && ip_addr_maskcmp(&iphdr->dest, &netif->ip_addr, &netif->netmask)) ||
                  ip_addr_cmp(&iphdr->dest, IP_ADDR_BROADCAST))
                  break;
  
          } /* end if */
  #if LWIP_DHCP
      if (!netif) {
          if (IPH_PROTO(iphdr) == IP_PROTO_UDP) {
              if (ntohs(
                      ((struct udp_hdr *)((u8_t *)iphdr + iphdrlen))->dest) == DHCP_CLIENT_PORT)
                  netif = inp;
          } /* end if */
      }     /* end if */
  #endif    /* LWIP_DHCP */
      if (!netif) {
  #if IP_FORWARD
          if (!ip_addr_isbroadcast(&iphdr->dest, &inp->netmask))
              ip_forward(p, iphdr, inp);
  #endif /* IP_FORWARD */
          pbuf_free(p);
          return ERR_OK;
      } /* end if */
  #if IP_REASSEMBLY
      if ((IPH_OFFSET(iphdr) & 0xFF3F) != 0) {
          p = ip_reass(p);
          if (p == NULL)
              return ERR_OK;
          iphdr = p->payload;
      }  /* end if */
  #else  /* IP_REASSEMBLY */
      if ((IPH_OFFSET(iphdr) & 0xFF3F) != 0) {
          pbuf_free(p);
          return ERR_OK;
      } /* end if */
  #endif /* IP_REASSEMBLY */
  #if IP_OPTIONS == 0
      if (iphdrlen > IP_HLEN) {
          LWIP_DEBUGF(IP_DEBUG | 2, ("IP packet dropped since there were IP options (while IP_OPTIONS == 0).\n"));
          pbuf_free(p);
          IP_STATS_INC(ip.opterr);
          IP_STATS_INC(ip.drop);
          snmp_inc_ipunknownprotos();
          return ERR_OK;
      }
  #endif /* IP_OPTIONS == 0 */
  #if LWIP_RAW
      if (!raw_input(p, inp)) {
  #endif /* LWIP_RAW */
  
          switch (IPH_PROTO(iphdr)) {
  #if LWIP_UDP
              case IP_PROTO_UDP:
              case IP_PROTO_UDPLITE:
                  snmp_inc_ipindelivers();
                  udp_input(p, inp);
                  break;
  #endif /* LWIP_UDP */
  #if LWIP_TCP
              case IP_PROTO_TCP:
                  snmp_inc_ipindelivers();
                  tcp_input(p, inp);
                  break;
  #endif /* LWIP_TCP */
              case IP_PROTO_ICMP:
                  snmp_inc_ipindelivers();
                  icmp_input(p, inp);
                  break;
              default:
                  /* send ICMP destination protocol unreachable unless is was a broadcast */
                  if (!ip_addr_isbroadcast(&(iphdr->dest), &(inp->netmask)) &&
                      !ip_addr_ismulticast(&(iphdr->dest))) {
                      p->payload = iphdr;
                      icmp_dest_unreach(p, ICMP_DUR_PROTO);
                  }
                  pbuf_free(p);
          }
  #if LWIP_RAW
      } /* LWIP_RAW */
  #endif
      return ERR_OK;
  }
  
  
  /* ip_output_if:
   *
   * Sends an IP packet on a network interface. This function constructs
   * the IP header and calculates the IP header checksum. If the source
   * IP address is NULL, the IP address of the outgoing network
   * interface is filled in as source address.
   */
  
  err_t ip_output_if(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest,
                     u8_t ttl, u8_t tos,
                     u8_t proto, struct netif *netif)
  {
      static struct ip_hdr *iphdr;
      static u16_t ip_id = 0;
  
      snmp_inc_ipoutrequests();
  
      if (dest != IP_HDRINCL) {
          if (pbuf_header(p, IP_HLEN)) {
              LWIP_DEBUGF(IP_DEBUG | 2, ("ip_output: not enough room for IP header in pbuf\n"));
  
              IP_STATS_INC(ip.err);
              snmp_inc_ipoutdiscards();
              return ERR_BUF;
          }
  
          iphdr = p->payload;
  
          IPH_TTL_SET(iphdr, ttl);
          IPH_PROTO_SET(iphdr, proto);
  
          ip_addr_set(&(iphdr->dest), dest);
  
          IPH_VHLTOS_SET(iphdr, 4, IP_HLEN / 4, tos);
          IPH_LEN_SET(iphdr, htons(p->tot_len));
          IPH_OFFSET_SET(iphdr, 0x0040);
          IPH_ID_SET(iphdr, htons(ip_id));
          ++ip_id;
  
          if (ip_addr_isany(src)) {
              ip_addr_set(&(iphdr->src), &(netif->ip_addr));
          } else {
              ip_addr_set(&(iphdr->src), src);
          }
  
          IPH_CHKSUM_SET(iphdr, 0);
          IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, IP_HLEN));
      } else {
          iphdr = p->payload;
          dest = &(iphdr->dest);
      }
  
  #if IP_FRAG
      /* don't fragment if interface has mtu set to 0 [loopif] */
      if (netif->mtu && (p->tot_len > netif->mtu))
          return ip_frag(p, netif, dest);
  #endif
      return netif->output(netif, p, dest);
  }
  /* ip_output:
   *
   * Simple interface to ip_output_if. It finds the outgoing network
   * interface and calls upon ip_output_if to do the actual work.
   */
  err_t ip_output(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest, u8_t ttl, u8_t tos, u8_t proto)
  {
  
      struct netif *netif;
  
      if (!(netif = ip_route(dest)))
          return ERR_RTE;
  
      return ip_output_if(p, src, dest, ttl, tos, proto, netif);
  
  } /* end ip_output */
  